I see. Thanks that is exactly what I was looking for. Would your example be an instance of an object-oriented approach, compartmentalizing things into functions?
On Wed, May 7, 2014 at 7:55 PM, Joe Cortes <escoz...@gmail.com> wrote: > Welcome to the wonderful world of generators! > > Looking at your code, you'll notice two things. First, you're > iterating over all the numbers twice: once to calculate them, and then > another time to actually do the sum. What's worse, at any given point > in time, you're only really using fibs[-1] and fibs[-2], and yet > you're still building this huge list with all the numbers. This is bad > in terms of memory efficiency. Luckily, it's such a common problem > that Python offers a really nice, really Pythonic solution. You can > define the following function: > > def fib(top): > first = 1 # As an aside, consider starting the sequence from 0, 1. > next = 2 > yield first > while next < top: > yield next > # For kicks, try rewriting the following three lines as a > tuple assignment. > new_next = next + first > first = next > next = new_next > > Now, how do you use this? This being Python, there is a super simple > way to do this: > > sum = 0 > for num in fib(4000000): > if num % 2 == 0: > sum += num > print sum > > > So, what's going on here? fib is mostly straightforward, but that > yield keyword might look new. > Here's the deal: when you have a function that uses the yield keyword, > that function becomes usable in the context of a for loop. Every time > it hits a yield it will, well, yield that value out to the for loop. > At the end of an iteration, control will be handed back to the > function, which will do its magic, and yield another value. Again, the > value will be sent out to the for loop, in this case as the "num" > variable, for use in that iteration. > When the function hits a return (or reaches the end of its body), the > for loop ends. > > This is called a generator function, and is a really nice way to > simplify and optimize your loops. > > You can read more about generators here: > https://wiki.python.org/moin/Generators > > > On Wed, May 7, 2014 at 7:27 PM, C Smith <illusiontechniq...@gmail.com> wrote: >> A topic came up on slashdot concerning "intermediate" programming, >> where the poster expressed the feeling that the easy stuff is too easy >> and the hard stuff is too hard. >> >> Someone did point out that 'intermediate' programming would still >> involve actually selling code or at least some professional >> experience, so this would probably fall into the category of 'novice'. >> >> I feel similarly right now and the cs 101 classes from udacity or >> coursera or the opencourseware stuff are very easy and boring. I tried >> the class "design of computer programs" on udacity and made it about >> halfway before being overwhelmed. The class involved making an api for >> a regex-like function to parse text (if I am communicating that >> correctly, it was sort of rewriting regex functionality in Python >> terms), and it seemed to go over a very definite cliff in terms of >> difficulty. Could someone provide a concise example of decorator use? >> >> Someone suggested projecteuler.net and I started blazing through >> things I had done before, when I realized this would be a good time to >> start more efficient practices instead of code that just happens to >> work and may be very inefficient. >> >> #sum all even fib seq integers under 4 million >> fibs = [1,2] >> sum = 0 >> while fibs[-1] < 4000000: >> nexty = fibs[-1] + fibs[-2] >> fibs.append(nexty) >> >> for xer in fibs: >> if xer%2 == 0: >> sum += xer >> print sum >> >> This gets the correct solution, but what would be ways to improve >> speed or use more complicated parts of Python to do the same thing. >> Thanks in advance >> _______________________________________________ >> Tutor maillist - Tutor@python.org >> To unsubscribe or change subscription options: >> https://mail.python.org/mailman/listinfo/tutor _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
